This invention claims benefit of Japanese Patent Application No. 2001-60556 filed on Mar. 5, 2001, the contents of which are incorporated by this reference.
The present invention relates to an endoscope system for observing fluorescent, and more particularly, to a light source device for irradiating an inspection object, or a subject, with an excitation light to induce fluorescence.
Generally, by irradiating organic tissue with an excitation light, the organic tissue can be made to generate fluorescence having a longer wavelength than that of the excitation light. A fluorophor in the body includes collagen, NADH (nicotinamide adenine dinucleotide acid), FAD (flavin adenine dinucleotide), pilus zinc nucleotide, etc. The details are described in xe2x80x9cUltraviolet Laser-Induced Fluorescence of Colonic tissuexe2x80x9d K. T. Schomacker et al., Lasers in Surgery and Medicine 12: 63-78 (1992).
In a combination of the phenomenon of generating fluorescence and fluorescence measuring techniques, tissue abnormality may be detected with high precision at a single cell level. Additionally, combining the fluorescence measuring techniques with endoscope techniques may provide a potential for diagnosing an early lesion which has been impossible to be detected by conventional endoscopes.
Connective tissue containing collagen resides substantially in the lower layer of mucosa, or submucosa. For example, when an endoscope transmits an excitation light from its lumen through the mucosa to excite the collagen, the fluorescence intensity to be induced is subject to the state, particularly the thickness, of the mucosa. Since cancer cells typically arise in the mucosa, the increased thickness of the mucosa caused by the grown cancer cells may attenuate the fluorescence. Thus, the position of the cancer cells may be identified to diagnose the lesion by measuring the attenuation of the fluorescence intensity. In this case, the collagen is typically excited by ultraviolet light or a blue component of visible light.
When the organic tissue is irradiated with ultraviolet light of 365 nm in wavelength, the organic tissue emits blue fluorescence having a peak at a wavelength of 460 nm due to NADH contained therein. The fluorescence intensity of NADH varies depending upon the oxidation-reduction state of NADH. In the tissue of low oxygen concentration, NAD (nicotinamide adenine dinucleotide) contained in the tissue is deoxidized and thereby the ratio of NADH is increased. Based on this, the fluorescence intensity of the tissue is increased.
Since the tissue of cancer cells, or cancerous tissue, is typically in an oxidation state, such tissue has a lower ratio of NADH and resultingly weaker fluorescence intensity. Thus, the cancerous tissue may be diagnosed by detecting this variance in the fluorescence intensity of NADH.
FIG. 13 shows a fluorescence spectrum of organic tissue irradiated with light of 365 nm in wavelength. As shown in FIG. 13, each fluorescence intensity of inflammatory tissue and cancerous tissue is lower than normal tissue. The same phenomenon will arise when organic tissue is irradiated with white light. FIG. 14 shows a reflection spectrum. As shown in FIG. 14, in a wavelength range of 400 to 600 nm, each reflection factor of inflammatory tissue and cancerous tissue is lower than normal tissue because the inflammatory tissue and cancerous tissue contain a larger amount of blood than that in the normal tissue. Japanese Patent Laid-Open Publication No. Hei 8-252218 discloses an endoscope adapted to selectively carry out visible light observation with the use of white light and fluorescent observation with the use of ultraviolet light by applying the above phenomenon.
Since fluorescent light, or fluorescence, detected by a fluorescent observation endoscope is weaker than the reflected light caused by irradiating with visible light, such fluorescent cannot be detected with a sufficient S/N ratio (signalxe2x80x94noise ratio) in regular endoscope observation. Thus, it is necessary to enhance the intensity of fluorescence to be detected. In order to improve this problem, it is effective to apply ultraviolet light of about 350 nm in wavelength to an excitation light. The conversion factor of the fluorescence resulting from exciting with the ultraviolet light is about ten times greater than that resulting from exciting with a blue component of visible light.
Conventional light source devices for endoscopes comprise a light source for emitting at least visible light between blue light and red light, an infrared cutoff filter for blocking infrared light, and a condenser lens for condensing light emitted from the light source at an incident end-face of a lightguide. The light emitted from the light source typically includes components of wavelengths other than that of visible light. Particularly, a xenon lamp may emit infrared light of 750 nm or more in wavelength with high energy. The light emitted from the light source is condensed at the incident end-face of the lightguide through the condenser lens. Then, light energy concentrated at the incident end-face of the lightguide is converted into thermal energy. The resultingly generated heat causes an undesirable high temperature at the incident end-face of the lightguide. In order to prevent this heat generation, the infrared cutoff filter is provided between the light source and the incident end-face of the lightguide to block infrared light. The infrared cutoff filter includes an infrared-cutoff interference filter composed of a transparent glass plate coated with a multilayer interference film and an infrared-cutoff absorption filter formed of a material capable of absorbing infrared light.
Japanese Patent Laid-Open Publication No. Hei 8-106059 discloses a method for dividing infrared light to block off the light in a particular frequency range. In this method, an interference filter and an absorption filter are disposed between a light source and an incident end-face of a lightguide. Spectral transmission factor properties of the infrared interference filter and infrared absorption filter are shown in the curves A and B of FIG. 15, respectively. Conventional infrared cutoff filters do not practically block light of 400 nm or less in wavelength and allow it to be transmitted therethrough. However, any transmission factor of an ultraviolet light region in the infrared interference filter is not specifically described. Further, as shown in FIG. 16, since the infrared interference filter has a sharp gradient of the transmission factor property around 350 nm in wavelength, the transmission factor in 350 nm in wavelength can be undesirably lowered to a large extent due to dispersion in manufacturing. In the interference filter, as compared with the transmission factor in the visible light region, the transmission factor in the ultraviolet light region is drastically lowered by a reflect action of the multilayer interference film and an absorption action of the material forming the multilayer interference film.
Thus, Japanese Patent Laid-Open Publication No. Hei 8-106059 merely discloses a technique for a regular light source optical system for endoscopes in which light of 400 nm or less in wavelength is not used and it is unnecessary to emit ultraviolet light, and describes a phenomenon that conventional infrared cutoff filters cannot sufficiently block light of about 400 nm in wavelength and resultingly allow it to be transmitted therethrough. However, when it is intended to positively emit ultraviolet light of 400 nm or less in wavelength (particularly, 350 nm in wavelength) with employing the infrared cutoff filter in a light source optical device for endoscopes, insufficient transmission factor of the ultraviolet light will be undesirably provided.
As described above, in the conventional infrared cutoff filters, ultraviolet light has a lower transmission factor than that of visible light. Consequently, when such infrared cutoff filters are applied to a light source for fluorescent observation endoscopes, ultraviolet light may not be sufficiently emitted.
In order to solve the aforementioned problems, it is an object of the present invention to provide a light source device for endoscopes capable of preventing an incident end-face of a lightguide from generating heat due to infrared light emitted from a light source, and capable of radiating sufficient ultraviolet light and visible light.
In order to achieve the above object, according to the present invention, there is provided a light source device for endoscopes for selectably applying fluorescent observation and reflection light observation with irradiation of blue to red visible light, said light source device comprising: a light source unit including a light source; a wavelength control filter; a condensing optics; and a lightguide, wherein the light source unit, the wavelength control filter, the condensing optics and the lightguide are linearly arranged along an optical axis, light from the light source unit includes at least light of ultraviolet wavelength and light of visible wavelength in the range of 400 to 650 nm and infrared wavelength when light from the light source unit is condensed at the light guide by the condensing optics, and the wavelength control filter is arranged between the light source and the lightguide, and the wavelength control filter transmits at least light of ultraviolet wavelength and visible light wavelength in the range of 400 to 650 and blocks light of infrared wavelength.
The objects of the present invention are also achieved by providing a light source device for endoscopes wherein the wavelength control filter satisfies the following conditions,
T350 greater than 0.6xe2x80x83xe2x80x83(1)
T400-650 greater than 0.8xe2x80x83xe2x80x83(2)
T800-950 less than 0.1xe2x80x83xe2x80x83(3)
where T350 is a transmission factor for 350 nm in wavelength, T400-650 is an average transmission factor for a wavelength range of 400 to 650 nm which is derived from averaging transmission factors measured in each 10 nm in a wavelength range of 400 to 650 nm, T800-950 is an average transmission factor for a wavelength range of 800 to 950 nm which is derived from averaging transmission factors measured in each 10 nm in a wavelength range of 800 to 950 nm.
The objects of the present invention are also achieved by providing a light source device for endoscopes wherein the wavelength control filter satisfies the following conditions,
T350 greater than 0.8xe2x80x83xe2x80x83(4)
T400-650 greater than 0.8xe2x80x83xe2x80x83(2)
T800-950 less than 0.1xe2x80x83xe2x80x83(3)
where T350 is a transmission factor for 350 nm in wavelength, T400-650 is an average transmission factor for a wavelength range of 400 to 650 nm which is derived from averaging transmission factors measured in each 10 nm in a wavelength range of 400 to 650 nm, T800-950 is an average transmission factor for a wavelength range of 800 to 950 nm which is derived from averaging transmission factors measured in each 10 nm in a wavelength range of 800 to 950 nm.
The objects of the present invention are also achieved by providing light source device for endoscopes wherein the wavelength control filter satisfies the following conditions,
T350 greater than 0.6xe2x80x83xe2x80x83(1)
T400-650 greater than 0.8xe2x80x83xe2x80x83(2)
T800-1200 less than 0.05xe2x80x83xe2x80x83(5)
where T350 is a transmission factor for 350 nm in wavelength, T400-650 is an average transmission factor for a wavelength range of 400 to 650 nm which is derived from averaging transmission factors measured in each 10 nm in a wavelength range of 400 to 650 nm, T800-1200 is an average transmission factor for a wavelength range of 800 to 1200 nm which is derived from averaging transmission factors measured in each 10 nm in a wavelength range of 800 to 1200 nm.
The objects of the present invention are also achieved by providing a light source device for endoscopes which further includes a means for blocking light of 330 nm or less in wavelength.
The objects of the present invention are also achieved by providing a light source device for endoscopes wherein the wavelength control filter is a transmission interference filter.
The objects of the present invention are also achieved by providing a light source device for endoscopes wherein the wavelength control filter includes a transmission interference filter and a transmission absorption filter.
The objects of the present invention are also achieved by providing a light source device for endoscopes wherein the wavelength control filter includes a transmission absorption filter and a transmission interference thin film provided on the surface of the transmission absorption filter.
The objects of the present invention are also achieved by providing a light source device for endoscopes, which further includes a color separating filter provided between the light source unit and the lightguide.
The objects of the present invention are also achieved by providing a light source device for endoscopes wherein the wavelength control filter includes three or more reflection surfaces, and is adapted to inflect the optical axis therein.
The objects of the present invention are also achieved by providing a light source device for endoscopes wherein the wavelength control filter is a reflection interference filter.
The objects of the present invention are also achieved by providing a light source device for endoscopes wherein the wavelength control filter includes a reflection interference filter and a transmission absorption filter.
The objects of the present invention are also achieved by providing a light source device for endoscopes wherein the wavelength control filter includes a reflection interference filter and a transmission interference filter.
The objects of the present invention are also achieved by providing a light source device for endoscopes wherein the single light source includes a light emission part and a reflector.
The objects of the present invention are also achieved by providing a light source device for endoscopes wherein the reflector has an ellipse shape.
The objects of the present invention are also achieved by providing a light source device for endoscopes wherein the reflector has a parabola shape.
The objects of the present invention are also achieved by providing a light source device for endoscopes wherein the light guide has an incident end-face, wherein the incident end-face is adjustably located at a position where ultraviolet light is condenses by the condensing optics.
The objects of the present invention are also achieved by providing a light source device for endoscopes wherein the light guide has an incident end-face, wherein when the transmission interference filter is arranged along the optical axis to allow fluorescent observation to be conducted, the incident end-face of the lightguide is adjustably located at a position where ultraviolet light is condenses by the condensing optics, and when the transmission interference filter is spaced apart from the optical axis to allow visible light observation to be conducted, the incident end-face of the lightguide is adjustably located at a position where visible light is condenses by the condensing optics.
The objects of the present invention are also achieved by providing a light source device for endoscopes wherein the wavelength control filter is an interference filter including an amorphous thin film.
The objects of the present invention are also achieved by providing a light source device for endoscopes wherein the interference filter is formed by laminating at least two groups of the amorphous thin films, wherein one group of the amorphous thin film has a high refractive index and includes at least one component selected from the group consisting of Sc2O5, Ta2O5, HfO2 and ZrO2, and another group of the amorphous thin film has a low refractive index and included at least one component selected from the group consisting of SiO2 and MgF2.